Influence of film thickness in THz active metamaterial devices: A comparison between superconductor and metal split-ring resonators

We experimentally demonstrate thickness-dependent resonance tuning in planar terahertz superconducting metamaterials. Inductive-capacitive resonance of arrays of split-ring resonators fabricated from 50, 100, and 200 nm thick YBa₂Cu₃O_7-δ (YBCO) and gold films were characterized and compared as a function of temperature. In the YBCO metamaterials the resonance frequency strongly depends on the thickness, and they show high thermal tunability in both resonance strength and frequency below the superconducting transition temperature, where the imaginary conductivity varies by three orders of magnitude. In contrast, the resonance in the gold metamaterials exhibits little thickness-dependence and very small tunability.